The bonding of carbon fibres to epoxy resins as affected by the manufacturing and surface treatment processes

The differences in the bonding to epoxy resins, as measured by the interlaminar shear strength (ILSS), of three nominally similar carbon fibres were related to differences in the manufacturing and surface treatment operations. Two of the fibres (denoted A and C) were determined to have emerged from the manufacturing process essentially identical, with the same crystal length, electrical resistivity and diameter. However, the subsequent surface treatments were very different, which resulted in different surface compositions (as measured by Auger electron spectroscopy), and a higher ILSS value for the composite made from fibre A as compared with one made from fibre C. By contrast, fibre B emerged from the manufacturing process differing slightly from fibres A and C, as determined by different graphite crystal lengths, electrical resistivities and diameters. Fibre B was found to be more ordered, and thus less susceptible to surface treatment, than for example fibre A. The ILSS value of the composite made from fibre B was lower than the value for the composite made from fibre A.